Fire alarm system having a diode coupled checking circuit means

ABSTRACT

A FIRE ALARM SYSTEM INCLUDING A PLURALITY OF FIRE ALARMS ARRANGED IN GROUPS. ALARM-SIMULTING CONDITIONS ARE PRODUCED IN EACH FIRE ALARM BY AN ELECTRIC TEST SIGNAL, THE RESPONSE OF EACH FIRE ALARM BEING SENT TO AN EVALUATION DEVICE AT A CENTRAL SIGNAL STATION THROUGH A LOGIC CIRCUIT COUPLING THE FIRE ALARMS TOGETHER.

Feb.16, 1971 BWALTHARDETAL 3,5641'524 FIRE ALARM SYSTEM HAVING A DIODECOUPLED CHECKING CIRCUIT MEANS Filed May 1967 United States Patent @HiceU.S. Cl. 340-214 Claims ABSTRACT OF THE DISCLOSURE A re alarm systemincluding a plurality of tire alarms arranged in groups.Alarm-simulating conditions are produced in each tire alarm by anelectric test signal, the response of each re alarm being sent to anevaluation device at a central signal station through a logic circuitcoupling the re alarms together.

BACKGROUND OF THE INVENTION The present invention relates to an improvedre alarm system comprising a central signal station to which electric realarms are connected in groups, wherein the number of conductors betweenthe central signal station and the fire alarms is independent of thenumber of re alarms. Furthermore, the inventive re alarm systemadditionally includes an apparatus for producing electrical test signalsby means of which alarm-simulating conditions are produced at the tirealarms which, in turn, bring about an electrical change in condition atan intact iire alarm, and further, the inventive system includes anapparatus for evaluating such changes and conditions.

In re alarm installations, there generally exist the requirements ofchecking the operational reliability of the individual re alarms atregular intervals. To this end, and in accordance with a workablemethod, alarmsimulating conditions are manually delivered to theindividual fire alarms one after the other or in series. The response ofthe relevant alarm is controlled at its locality or at the centralstation. However, this technique is, above all, extremely time-consumingand uneconornical, if the installation consists of a larger number oftire alarms, for instance, one hundred re alarms or more. In such case,a regular manual monitoring at shorter time intervals can no longer comeunder consideration for practical reasons.

It is for these reasons that methods have been developed in which it ispossible to achieve from the central station alarm-simulating conditionsat the tire alarms through use of special electronic means, and to checkthe response conditions of all re alarms at the central station. Thediculty with such method, above all, resides in the reliabledetermination of whether all tire alarms of a group have actuallyresponded.

In a known system, a separate conductor is led from each tire alarm backto the central station. During the checking operation, a signal appearsat such conductor which is characteristic of the response condition ofthe 3,564,524 Patented Feb. 16, 1971 relevant fire alarm. This systemhas the drawback that it requires extensive additional installations,which becomes of particular importance if such a monitoring deviceshould be subsequently installed in an already existing re alarm system.

Consequently, it is desirable to provide a monitoring device in whichthe number of conductors leading from the central station to the realarms is independent of the number of connected re alarms. In a knownarrangement of this type, all of the tire alarms are simultaneouslycaused to respond from the location of the central station. Further, bymeans of a current measuring device at the central station which isprovided at one of both current delivery conductors of the fire alarm,the response of all tire alarms is monitored, whereby there is checkedthe coincidence of the total current with some predetermined referencevalue. Apart from the great current consumption which has an adverseeitect upon the choice and dimensioning of the conductors, the networkdevices, the emergency power groups, etc., this arrangement is limitedto groups having relatively few tire alarms. Because of the diversity ofthe electrical characteristics of the structural elements in the realarms as well as because of the limited measuring accuracy duringcomparison of the total current with the reference value based upon ananalogous measurement, this technique is unreliable with a larger numberof tire alarms and often times results in false alarms.

SUMMARY O'F THE INVENTION Accordingly, it is a primary object of thepresent invention to provide an improved monitoring device for a realarm system of the previously mentioned type in which it is possible toreliably check or monitor an optional large number of re alarms pergroup.

It is another object of the present invention to provide a monitoringsystem which may be installed in existing re alarm systems.

It is a further object of the present invention to provide a monitoringsystem which requires low additional power.

It is an additional object of the present invention to provide amonitoring system which makes use of digital techniques.

Generally speaking, the present invention is characterized by thefeatures that the tire alarms of a group are coupled with one another bymeans of a logic circuit and that the logic circuit, during the checkingoperation, then delivers a signal to the evaluation device when all tirealarms of a group have responded (AND-gate) or at least one re alarm hasnot responded (OR-gate).

A number of diierent embodiments of the invention as well as furtherinventive features will be described in greater detail hereinafter inconjunction with the figures of the drawing. In this regard, it will beappreciated that while the exemplary fire alarm installations depictedherein are in each instance equipped with ionization re alarms, it wouldbe equally well possible to also employ optical llame detecting alarms,smoke detecting alarms or temperature detecting alarms.

BRIEF DESCRIPTION OF THE DRAWING The invention will be betterunderstood, and objects other than those set forth above, will becomeapparent,

when consideration is given to the following detailed descriptionthereof. Such description makes reference to the annexed drawingwherein:

FIG. 1 illustrates a circuit diagram of a first embodiment of theinvention in which the individual lire alarms have associated therewithdiode means for coupling the individual vfire alarms to one another; and

yFIG. 2 is a circuit diagram of an exemplary embodiment of the inventionin which the individual tire alarms have associated therewithoscillation generators.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawing, in.FIG. 1 there are depicted two fire alarms 39 and 40 of identicalconstruction. These lire alarms 39 and 40 are connected parallel to oneanother via the supply conductors or leads 35 and 36 as well as beingconnected Lvia an additional signal conductor 29 with a central station41. As already remarked, these re alarms 39 and 40 are of identicalconstruction and preferably consist of two ionization chambers 21 and22, the air content of which can be rendered completely or partiallyconductive through an appropriate radioactive preparation as is known inthe art. Furthermore, these tire alarms 39 and 40 each incorporate aswitch element 23 which, in this case, is a ieldeffect transistor. Theionization chamber 21 operates as a measuring chamber, whereas theionization chamber 22 is used as a reference chamber. `Chamber 22 can bereplaced by a high-ohm resistor or an equivalent high ohm element.Likewise, in lieu of a field-effect transistor 23 it is possible to useother semi-conductor devices or a diderent switch element with high-ohminput resistance or impedance, for instance a cold-cathode tube.

The drain or anode of the field-effect transistor 23 is connected via aresistor 25 with the negative supply conductor 35, the cathode or sourcevia the tap of a potentiometer 24 with the positive supply conductor 36.Furthermore, at the drain or anode of the field-effect transistor 23there is connected the gate of a controlled rectifier 26, the cathode ofwhich is coupled with the negative supply conductor 35 and the anode ofwhich, on the one hand, is connected via a resistor 44 to the negativesupply conductor 35 and, on the other hand, via a resistor 45 with thepositive supply conductor 36. The anode of the controlled rectifier 26is furthermore connected with the signal conductor 29 through the seriescircuit or connection incorporating the indicating lamp 31 and the Zenerdiode 28. A resistor 34 is connected parallel with the indicating lamp31. This resistor 34 maintains the connection between the controlledrectifier 26 and the Zener diode 28 during breakdown of the indicatinglamp 31.

The potential at the tap of the potentiometer 24 is adjusted in such amanner that the tield-etect transistor 23 and thereby the controlledrectier 26 block in the normal condition. The signal conductor 29 isconnected at the central station 41 via a contact of the switch 43 and aresistor with the positive pole of the voltage source designated byreference numeral 100. The Zener voltage of the diode 28 is selected insuch a manner that when the rectitier 26- is blocked, in which case itsanode has a potential determined by the voltage divider 44, 45, thisdiode 28 likewise blocks.

The signal conductor 29 is then without current and the voltage at point200 equals the voltage of source 100.

Now if combustion gas enter the measuring the measuring chamber 21, thenthe field-effect transistor 23 and the controlled rectifier 26 changetheir switched condition. More precisely, the potential at the anode ofthe controlled rectifier 26 practically drops to that of the supplyconductor (ground), so that the voltage across the diode 28 now exceedsthe Zener voltage and the diode begins to conduct. At the centralstation 4.1 the point 200 or voltage at point 200 or the contact of theswitch 43 drops from the value voltage of source 100 to a new valueapproximately corresponding to the Zener Voltage ot' the diode 28. In sodoing, the resistor 30 is selected in such a manner that the currentflowing through the indicating lamp 31 initially does not cause such tolight up or indicate. By closing a switch 33 arranged parallel theresistor 30, the indicating lamp 31, in the case of the alarm, can becaused to ignite from the central station, whereby the tire alarmreceives a receipt or acknowledgement of the proper reception of thealarm signal at the central station.

The Zener diodes 28 of the individual tire alarms commonly form, in thenormal operating condition, an OR- gate, whereby an alarm signal of theone or other fire alarm arrives via the common conductor at the centralstation without having any etect upon the remaining ire alarms. Inaccordance with the invention, the OR-gate is coupled or switched duringthe checking operation in such a manner that a signal only appears inthe central station if at least one tire alarm has not responded. Thiscan be realized in that, the conductor 29 is supplied by a voltagesource 300 by means of the switch 43. The value of voltage source 300 issmaller than the Zener voltage otthe diodes 28. Since voltage of source300 is smaller than voltage of source 100, the Zener diodes 28 are poledin the forward direction via the resistor 45 and the indicating lamps.31 and a current tiows through the signal conductor. Thealarm-simulating conditions are produced through opening for a shorttime the switch 37 to thus introduce a voltage reducing Zener diode 38in the supply conductor 36 which initially causes the capacitor 42 topartially discharge. Upon closing of the switch 37, a momentaryover-voltage is produced be tween the gate and cathode of theiield-etfect transistor 23. The alarm-simulating conditions thus bringabout a. response of the held-effect transistor 23 and thereby thecontrolled rectifier 26. Then, as a practical matter, the voltage ofsource 300 appears across the Zener diodes 28 of the intact tire alarms,which Voltage of source 300 by definition is smaller than the Zenervoltage. If all of the tire alarms of a group have properly respondedthen the conductor 29 is without current. On the other hand, a signalappearing at the conductor 29 means that one or more tire alarms havenot responded.

The return of the iire alarm can likewise take place by means of thesignal conductor 29. To this end, the switch 43 is thrown or applied fora short time to a negative voltage source 400.

Naturally, it is also possible to apply numerous rnoditications to thecircuit of FIG. l. Thus, for instance, it is possible to employconventional diodes instead of Zener diodes, whereby the measures whichmust be undertaken in such case will be apparent to those skilled in theart.

FIG. 2 depicts a circuit diagram of an embodiment of the invention whichis essentially based upon the same principles as the circuit diagram ofFIG. 1. In this circuit arrangement the individual fire alarms areconnected with one another into a logical circuit and an additionalsignal conductor is dispensed with.

By referring to FIG. 2 in greater detail it will be recognized that theindividual lire alarms 50 embody a measuring ionization chamber 52 and areference ionization chamber 54, the common connection point of which iscoupled with the starter electrode of a cold-cathode tube 56. The anodeof the cold-cathode tube 56 is coupled via a resistor 58 with the supplyconductor 60, and the cathode is directly connected with the supplyconductor 62. Furthermore, between both of the conductors 62 and 60 aseries connection of a capacitor 64 and a resistor 66 is disposed. Atthe common juncture point or point of connection of the capacitor 64 andthe resistor 66 one electrode of the measuring ionization chamber 52 isconnected. The diode 68 is connected in parallel with the resistor 66.Finally, the anode of the cold-cathode tube 56 is connected via aresistor 70 with the connection point of a series connection of afurther capacitor '72 and a glow-discharge tube 74 disposed between thesupply conductors 60 and 62. Glow-discharge tube 74, capacitor 72 andresistors 58 and 70 form an impulse transmitter. A current flows throughthe glow-discharge tube 74 which charges the capacitor 72 for suchlength of time until the voltage is dropped via the glow-discharge tube74 to the extinguishing voltage, whereafter the capacitor 72 dischargesvia the resistor 58 and 70. As a result, the voltage across theglow-discharge tube 74 again increases until it reaches the ignitionvoltage, and a new cycle is initiated. The individual current surges canbe registered at the secondary winding of a transformer 76 provided inthe supply conductor 62 at the central station 78.

If combustion gases enter the measuring ionization chamber 52, then thecold-cathode tube 56 ignites because of an increase of the starterpotential and draws a current through the resistor 58. In the event theoperating voltage of the cold-cathode tube 56 is larger than theignition voltage of the glow-discharge tube 74 then the oscillations ofthe associated impulse transmitter 74, 70, 72 stop. The current surgeduring ignition of the cold-cathode tube 56 can be employed in knownmanner for triggering a relay `80 or another alarm-transmitting device.

The checking operation is initiated by dropping the supply voltage 500for a short period of time. In so doing, the capacitor 64 dischargesduring the reduction in voltage across the diode 68 to the new supplyvoltage. Now, if the supply voltage 500 is instantaneously increasedagain to the old value, then the diode 68 once again blocks and thecapacitor 64 slowly charges via the high-ohm resistor `66. In so doing,however, the potential at the starter of the cold-cathode tube 56initially is at an increased value determined by the capacitor 64 andthe series connection incorporating the ionization chamber 52-54 and theresistor 53. The value of this potential is measured in such a mannerthat the coldcathode tube igntes. 'Ihe saw-tooth oscillations stop inthe intact tire alarms, so that a signal only appears at the secondarywinding of the transformer 76--which at the same time forms the input ofa valuation circuit or device 19-when one or more re alarms have notresponded. Consequently, the transformer 76 provides in such case animpulse-type OR-gate.

After completion of the checking operation, the supply voltage 500 isdropped slightly below the operating voltage of the tube 56 andthereafter slowly again increased to the full value.

-In each case, the checking operation is repeated at appropriate timeintervals.

While there is shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied and practicedwithin the scope of the following claims.

Accordingly, what is claimed is:

1. A ire alarm system comprising:

a plurality of tire alarms connected in parallel together in at leastone group;

a central signal station;

conductor means connecting said central signal sta- .tion with saidplurality of fire alarms, the number of said conductors beingindependent of the number of said re alarms of each group;

means for generating an electric test signal during an alarm checkingoperation;

said re alarms including means responsive to said electric test signalto produce alarm-simulating conditions;

means connecting each of said plurality of fire alarms of at least onegroup to said central signal station, said means including diodecoupling circuit means for producing no alarm-checking response signalswhen all ire alarms of a group have responded to said electric testsignal and producing an alarmchecking response signal when at least onere alarm of a group has not responded to said electric test signal; and

means for sensing at least one of said respective response signals.

2. A fire alarm system as claimed in claim 1, wherein said diodecoupling circuit means includes diodes which are coupled .to a commonconductor connected to said diode coupling circuit means and to saidcentral signal station; said fire alarm system further including meansfor applying a lrst voltage to said common conductor during said alarmchecking operation.

3. A re alarm system as claimed in claim 2, wherein said diodes compriseZener diodes and wherein said first voltage is of a value less than thebreakdown voltage of said Zener diodes.

4. A fire alarm system as claimed in claim 2, further including meansfor applying a second voltage to said common conductor during normalalarm operation, said diode coupling circuit means producing an actualalarmchecking response signal at said central signal station when atleast one re alarm is actuated.

5. A re alarm system as claimed in claim 4, wherein said diodes compriseZener diodes and wherein said second voltage is of a value greater thanthe breakdown voltage of said Zener diodes.

6. A re alarm system as claimed in claim 2, wherein a visual indicatingelement is provided for each tire alarm, said visual indicating elementsbeing connected between said re alarms and said diodes included in saiddiode coupling circuit means, said visual indicating elements having acurrent threshold value below which they will not indicate.

7. A ire alarm system as claimed in claim 6, further including anadditional voltage source, said additional voltage source being providedat said central signal station; resistance means connected between saidadditional voltage source and said common conductor, said resistancemeans limiting current flow to said visual indicating element of anactuated re alarm to a value less than the threshold value of saidvisual indicating element; and switch means tor short-circuiting saidresistance means thus causing current to ilow to said indicating elementhaving a value greater than said threshold value.

8. A tire alarm system as claimed in claim 2, including a source ofnegative voltage and means for resetting said plurality of tire alarmsaftercompletion of said alarm checking operation, said means forresetting including switch means for connecting said common conductorwith said source of negative voltage.

9. A re alarm system as claimed in claim 2, further including:

a positive and a negative supply conductor;

a measuring ionization chamber and a reference ionization chamberconnected in series across said positive and negative supply conductors;

a eld-eiect transistor having a drain, a source and a gate electrode;

a first resistor;

a variable resistor;

means connecting said drain of said eld-eifect transistor to saidnegative supply conductor through said rst resistor;

means connecting said source of said field-effect transistor to saidpositive supply conductor through said variable resistor;

means connecting said gate of said field-effect transistor to thejunction of said measuring ionization chamber and said referenceionization chamber;

a controlled rectien'having an anode, a cathode and a gate;

a second resistor;

means connecting said anode of said controlled recf References Citedtifier to said positive supply conductor through said Y UNITED STATESPATENTS second resistor; means connecting said gate of said controlledrectier 215891869 3/1952 Rum@ 340-214 to said drain of said field-effecttransistor; 5 2,647,237 7/1953 Herbst 340214 means connecting saidcathode of said controlled rec- 3,099,824 7/ 1963 Vitt 340-214 tier tosaid negative supply conductor; and 3,248,721 4/1966 Cockrell 340-214 avisual indicating element connected ibetween said 3,278,920 10/1966Sargent 340-214 anode of said controlled rectifier and the associated3,422,414 1/1969 Margreiter AF 340 214 diode of said diode couplingcircuit means. 10 10. A re alarm system as claimed in claim 9, furtherTHOMAS B HABECKER, primal-y Examiner including a capacitor in parallelwith said reference ionization chamber and wherein said electric testsignal U.S. Cl. X.R. comprises a reduction in potential of said positivesupply 340-228 conductor.

